Circadian Rhythm & Sleep Mechanics

Sleep Cycle Calculator & Stages

Sync your alarm with human biological 90-minute sleep intervals. Never get abruptly yanked out of Stage 3 deep sleep again.

I Need To Wake Up At:

Calculates 90-minute sleep cycles plus an average 15 minutes to fall asleep.

9 hrs (6 Cycles)

9:45 PM

Optimal Recovery (6 Cycles)

7.5 hrs (5 Cycles)Recommended

11:15 PM

Recommended Standard (5 Cycles)

6 hrs (4 Cycles)

12:45 AM

Minimum Functional (4 Cycles)

4.5 hrs (3 Cycles)

2:15 AM

Power Nap / Tight Schedule (3 Cycles)

N1 (Stage 1)

5% – 10% of total sleep

Drifting off. Heart rate and breathing slow down, muscles relax with occasional sudden twitches (hypnic jerks).

If Woken Up:Easy to wake up. You may feel like you were never truly asleep.

N2 (Stage 2)

45% – 55% of total sleep

Body temperature drops, eye movement stops, and brain filters outside noises to consolidate memory.

If Woken Up:Refreshed if waking at the end of a full 90-minute cycle.

N3 (Stage 3)

15% – 25% of total sleep

Physical tissue repair, bone/muscle building, human growth hormone (HGH) release, and immune system replenishment.

If Woken Up:TERRIBLE (Sleep Inertia). Waking up directly during N3 leaves you feeling foggy, dizzy, and disoriented for an hour.

REM Sleep

20% – 25% of total sleep

Vivid dreams occur. Skeletal muscles are temporarily paralyzed (atonia) so you don’t act out dreams. Emotional processing and creativity.

If Woken Up:Alert and mentally sharp, often recalling vibrant dreams.